ALLEN PARK, Mich.—There are plenty of reasons the Lions have gone from one of the most disappointing teams in the league after four games to a viable NFC playoff contender after eight.

Their patchwork secondary has overachieved on a regular basis despite starting a different four every week. Their special-teams woes of September disappeared after October’s bye. And most importantly, Matthew Stafford has regained his form from a breakout 2011.

Stafford has played his best football of the season during the Lions’ current two-game win streak. He led the ninth late game-winning drive of his career and third of the year in a victory over the Seahawks, and was even crisper than his numbers would suggest (22 of 33 passing, 285 yards) last week against the Jaguars.

Stafford’s biggest strides this year have come on third downs, where he’s had to spread the ball to receivers other than Calvin Johnson because of the way defenses have played.

In the last two weeks, Stafford has completed 23 of 27 third-down passes and converted a whopping 19 (70 percent) into first downs—11 on third-and-7 or longer. He’s thrown two third-down touchdowns the last two weeks, had a third dropped and ran in another score.

Johnson is playing with a sore knee that he expects to be an issue the rest of the year, so the Lions need Stafford to continue his clutch ways during a treacherous second half that includes seven of eight games against opponents with winning records.